Transistor circuit, display panel and electronic apparatus

ABSTRACT

A transistor circuit is provided including a driving transistor where conductance between the source and the drain is controlled in response to a supplied voltage, and a compensating transistor where the gate is connected to one of the source and the drain, the compensating transistor being connected so as to supply input signals to the gate of the driving transistor through the source and drain. In a transistor circuit where conductance control in a driving transistor is carried out in response to the voltage of input signals, it is possible to control the conductance by using input signals of a relatively low voltage and a variance in threshold characteristics of driving transistors is compensated. With this transistor circuit, a display panel that can display picture images with reduced uneven brightness is achieved.

This is a Divisional of U.S. patent application Ser. No. 10/384,756filed on Mar. 11, 2003, which is a Divisional of U.S. patent applicationSer. No. 10/067,763 filed on Feb. 8, 2002, which is a Divisional of U.S.patent application Ser. No. 09/424,043 filed on Nov. 18, 1999, which isa National Phase of PCT Application No. JP 99/01342 filed on Mar. 17,1999, which are hereby incorporated by reference in their entirety. Thisapplication claims priority to Japanese Patent Application No. 10-69147filed Mar. 18, 1998, which is hereby incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the technical field of transistor circuitsincluding a plurality of transistors such as thin-film transistors(mentioned as TFT hereafter), field effect transistors and bipolartransistors, and particularly relates to the technical field oftransistor circuits including driving transistors for controllingdriving current, by controlling conductance between the source and thedrain in response to voltage supplied to the gate, that is supplied to adriven element such as a current-controlled (current-driven) elementthrough the source and the drain.

2. Description of Related Art

Generally, the voltage/current characteristics and thresholds oftransistors tend to vary, depending on various conditions such as thequality and thickness of semiconductor films, impurity concentration anddiffusion areas, the quality, thickness and the like of gate insulatingfilms, operating temperature, and the like. In the case of bipolartransistors consisting of crystal silicon, the variance of thresholds isrelatively small, but in the case of TFTs, the variance is usuallylarge. Particularly, in the case of TFTs formed in a wide range inplurality on a TFT array substrate in a display panel such as a liquidcrystal panel, an EL panel, and the like, the variance involtage/current characteristics and thresholds often becomes extremelylarge. For instance, when such TFTs are manufactured so as to set thethreshold at about 2V (+2V in the case of N channel, and −2V in the caseof P channel), the variance is sometimes about several ±V.

In the case of a voltage-controlled (voltage-driven) type transistor forcontrolling the voltage of picture elements made of liquid crystals orthe like, such as a so-called TFT liquid crystal panel, the variance involtage/current characteristics and thresholds of driving TFTs that areapplied to each picture element is not likely to be a problem. In otherwords, in this case, even if there is a slight variance in thevoltage/current characteristics and thresholds of TFTs, contrast andbrightness of each picture element can be controlled at high precisionby increasing the precision of the voltage supplied to each pictureelement from the outside through the TFTs only if there is enoughswitching time. Therefore, even in the case of a TFT liquid crystalpanel or the like for display wherein contrast and brightness at eachpicture element are regarded as important, high grade picture images orthe like can be displayed by TFTs with a relatively large variance ofvoltage/current characteristics and thresholds.

On the other hand, display panels have been recently developed thatinclude current-controlled light-emitting elements, such as a selflight-emitting organic ELs to change the brightness at picture elementsin response to current supply. These display panels have receivedattention as display panels that can display picture images without backlight and reflected light, that consume less power, being less dependenton the angle of view, and are sometimes flexible. Even in this EL panel,a driving TFT is used at each picture element for driving an activematrix. For instance, it is constructed so as to control (change) thedriving current supplied to an EL element from power source wiringconnected to a source in response to the voltage of data signals appliedto a gate, by connecting the drain of a driving TFT to the EL elementthrough a hole-injecting electrode. Using a driving TFT as mentionedabove, driving current flowing to an EL element can be controlled bycontrolling conductance between a source and a drain in response to thevoltage change of input signals, so that brightness at each pictureelement can be changed for picture image display and the like.

However, particularly in the case of the current-controlled element suchas the EL panel mentioned above, the variance of voltage/currentcharacteristics and thresholds tends to be a problem in the driving TFTat each picture element. In other words, in this case, even if thevoltage precision of data signals supplied to the driving TFTs from theoutside is enhanced to some extent, the variance in voltage/currentcharacteristics and thresholds in the driving TFTs appears directly asthe variance of the driving current supplied to data signals, thusreducing the precision of the driving current. As a result, thebrightness at each picture element is likely to vary in accordance withthe variance in thresholds of the driving TFTs. Moreover, especiallywith current manufacturing techniques of low temperature polysiliconTFTs, voltage/current characteristics and thresholds vary considerably.Thus, this problem is, in practicality, extremely serious.

If each TFT is manufactured so as to reduce the variance involtage/current characteristics and thresholds in consideration of thisproblem, the yield will decline and, particularly in the case of anapparatus with a display panel having a plurality of TFTs, the yieldwill decrease a great extent, and thus opposing a general goal of lowercosts. Alternatively, it is almost impossible to manufacture TFTs thatcan lower such a variance. Moreover, even if a circuit for compensatingthe variance of voltage/current characteristics and thresholds at eachTFT is installed separately, the apparatus will be complex and large,and moreover, the consumption of electric power will increase.Particularly, in the case of a display panel wherein a plurality of TFTsare arranged at high density, the yield will decline again or it will bedifficult to satisfy current demands such as lower power consumption,and miniaturization and lightening of an apparatus.

This invention is carried out in consideration of the above-notedproblems, and aims to provide transistor circuits for controllingconductance in driving transistors in response to the voltage of inputsignals, the conductance of which can be controlled by relatively smallinput signals and that can compensate for the variance involtage/current characteristics and thresholds of driving transistorswith somewhat smaller power consumption by using a relatively smallnumber of transistors, and a display panel and an electronic apparatususing the same.

In this invention, the following transistor circuits according to thefirst to tenth aspects are provided.

First, according to a first aspect of the invention a transistor circuitis characterized in that it includes a driving transistor having a firstgate, a first source and a first drain, wherein conductance between thefirst source and first drain is controlled in response to the voltage ofinput signals supplied to the first gate, and a compensating transistorhaving a second gate, a second source and a second drain, wherein thesecond gate is connected to one of the second source and second drain,and wherein the compensating transistor is connected to the first gatein an orientation so as to supply the input signals to the first gatethrough the second source and second drain, and to allow the first gateto move electric charge into a direction to lower the conductance.

According to the above-noted transistor circuit of the first aspect ofthe invention, one of the second source and second drain of thecompensating transistor is connected to the first gate of the drivingtransistor, and input signals are supplied to the first gate of thedriving transistor through this second source and second drain. Then, atthe driving transistor, the conductance between the first source andfirst drain is controlled in response to the voltage of input signalssupplied to the first gate. Herein, the compensating transistor has thesecond gate connected to the second drain, and is connected to the firstgate in an orientation to allow the first gate to move electric chargeinto a direction to lower the conductance between the first source andfirst drain. In other words, the compensating transistor has diodecharacteristics and when the driving transistor is, for example, anN-channel type transistor, current can be carried from the first gateinto the direction of an input signal source. Alternatively, when thedriving transistor is a P-channel type transistor, current can becarried from an input signal source to the direction of the first gate.

Therefore, as input signals are supplied to the transistor circuit, thegate voltage of the first gate, compared with the voltage of inputsignals at the time of being input to the compensating transistor, risesto the side of increasing the conductance of the driving transistor onlyby a threshold level of the compensating transistor. As a result, inorder to obtain preferable conductance in the driving transistor, inputsignals of a voltage that is lower only by a threshold (voltage) levelof the compensating transistor, instead of the gate voltagecorresponding to the conductance, can be supplied through thecompensating transistor. In this way, since the gate voltage in responseto input signals can rise only by a threshold (voltage) of thecompensating transistor, equivalent conductance control can be carriedout by the lower voltage of input signals compared with the case of nocompensating transistor.

These input signals are generally at a high frequency relative to othersignals, and the consumption of electric power can be reducedsignificantly if lower input signals can be used.

Moreover, setting a gate voltage at the first gate by increasing thevoltage of input signals from the compensating transistor as mentionedabove indicates that, when seen as a transistor circuit as a whole, thethreshold of input signals supplied to a driving current flowing througha source and a drain whose conductance is controlled in the drivingtransistor is lower than the threshold voltage of the driving transistoronly by the threshold voltage of the compensating transistor as avoltage increases from the input voltage to the gate voltage. In otherwords, within the threshold of input voltage supplied to a drivingcurrent, the threshold of the compensating transistor and the thresholdof the driving transistor are offset from each other. Therefore, bymaking the threshold characteristics and the voltage/currentcharacteristics of both transistors similar to each other, it ispossible to set the threshold of input signals to driving current tozero.

Moreover, by offsetting the threshold of the driving transistor and thethreshold of the compensating transistor in the transistor circuit as awhole as mentioned above, the threshold of input signals can be setcloser to a constant level (zero) without depending on the level ofthreshold of the driving transistor. In other words, when a plurality oftransistor circuits is prepared by using many driving transistors withdifferent thresholds, a difference in thresholds between transistorcircuits is smaller than (or is ideally almost the same as) a differencein the thresholds of driving transistors by setting the thresholds ofthe driving transistor and the compensating transistor in eachtransistor circuit close to each other (ideally equal to each other).Thus, in preparing a plurality of transistor circuits, a plurality oftransistor circuits with almost or completely no variance in thresholdscan be provided even when many driving transistors with many differentthresholds are used.

According to a second aspect of the invention, the transistor circuitaccording to the first aspect mentioned above is characterized in thatit has a resetting means for supplying reset signals, having a voltagethat gives higher conductance than the maximum conductance controlled inresponse to the input signals, to a first gate before the input signalsare supplied.

According to the above-noted transistor circuit of the second aspect ofthe invention, before input signals are supplied to the first gate of adriving transistor (or after the input signals are supplied before thenext input signals are supplied), reset signals, having a voltage whichgives a higher conductance than the maximum conductance of the drivingtransistor controlled in response to input signals, are supplied to thisfirst gate by the resetting means. As a result, the gate voltage of thedriving transistor can be set constant without depending on the level ofvoltage of input signals. Moreover, it becomes possible to supply inputsignals to the first gate through the compensating transistor which isconnected to the first gate in an orientation to permit electric chargeto move into a direction so as to lower conductance after resetting.

According to a third aspect of the invention, the above-noted transistorcircuits according to any of the first and second aspects, ischaracterized in that the reset signals are set at a voltage higher thanthe maximum voltage of input signals by a threshold voltage level of thecompensating transistor.

According to the above-mentioned transistor circuit of the third aspectof the invention, reset signals having a higher voltage than inputsignals are supplied to the first gate of the driving transistor by theresetting means. Moreover, the voltage of these reset signals is sethigher than the maximum voltage of the input signals by a thresholdvoltage of the compensating transistor, so that a voltage higher thanthe voltage of the input signals by a threshold voltage level of thedriving transistor can always be supplied to the first gate of thedriving transistor through the compensating transistor, without beingdependent on the level of voltage of input signals or thresholds of thedriving transistor, when input signals are input after resetting.

According to a fourth aspect of the invention, the transistor circuitaccording to the second aspect mentioned above, is characterized in thatit includes a resetting transistor wherein the resetting means has athird gate, a third source and a third drain, wherein one of the thirdsource and the third drain is connected to the first gate, and whereinthe reset signals are supplied to the first gate through the thirdsource and third drain after reset timing signals are supplied to thethird gate before the supply of the input signals.

According to the above-noted transistor circuit of the fourth aspect ofthe invention, when reset timing signals are supplied to the third gateof the resetting transistor, reset signals are supplied to the firstgate of the driving transistor through the third source and third drainby the resetting transistor. As a result, the gate voltage of thedriving transistor can be reset at a constant by the timing of supplyingreset timing signals. Therefore, the operations that are explained forthe second transistor circuit become possible.

According to a fifth aspect of the invention, the transistor circuitaccording to any one of the first to the fourth aspects mentioned above,is characterized in that the driving transistor and the compensatingtransistor are the same type of transistors.

According to the transistor circuit of the fifth aspect of the inventionmentioned above, the driving transistor and the compensating transistorare the same type of transistors, but the “same type” means that theconductive type of transistors is the same herein. For instance, whenthe driving transistor is an N channel type transistor, the compensatingtransistor is also an N channel type transistor. With the drivingtransistor as a P channel type transistor, the compensating transistoris also a P channel type transistor. Therefore, the threshold of thecompensating transistor and the threshold of the driving transistorbecome almost equal to each other, so that these thresholds are offsetfrom each other in the transistor circuit. As a result, it becomespossible to carry out conductance control by setting the threshold ofinput signals supplied to a driving current to approximately zero.

Also, by providing the same transistor channel width, design valuesincluding a channel length, device structures, process conditions, andthe like to both the driving transistor and the compensating transistor,more complete compensation becomes possible.

According to the sixth aspect of the invention, the transistor circuitaccording to any of the above-noted first to the fifth aspects, ischaracterized in that the circuit further includes a switchingtransistor having a fourth gate, a fourth source and a fourth drain, andwherein the transistor is connected so as to supply the input signals tothe compensating transistor through the fourth source and fourth drainwhen switching timing signals are supplied to the fourth gate.

According to the above-noted transistor circuit of the sixth aspect,when switching timing signals are supplied to the fourth gate of theswitching transistor, input signals are supplied to the compensatingtransistor through the fourth source and fourth drain of the switchingtransistor. As a result, input signals can be supplied to the drivingtransistor by the supply timing of switching timing signals.

According to a seventh aspect of the invention, the transistor circuitaccording to any of the above-noted first to sixth aspects, ischaracterized in that it further includes a storage capacitor connectedto the first gate.

According to the transistor circuit of the seventh aspect, when inputsignals are supplied to the first gate, the voltage is held by thestorage capacitor connected to the first gate. Therefore, even wheninput signals are supplied only for a fixed period, the voltage at thefirst gate can be held over a longer period than the fixed period.

Also, even when there is leakage current in the switching transistorthrough the compensating transistor, it becomes possible to reduce thefluctuation of electric potential applied to the first gate.

According to an eighth aspect of the invention, the transistor circuitaccording to any of the above-noted first to seventh aspects, ischaracterized in that the transistors consist of thin-film transistorsformed on the same substrate respectively.

According to the transistor circuit of the eighth aspect, the effect ofvoltage/current characteristics and threshold characteristics of thedriving thin-film transistor, which is formed on the same substrate, ona driving current can be compensated by the compensating thin-filmtransistor. Particularly, as both thin-film transistors are formed onthe same substrate in the same thin-film forming process, thecharacteristics between both transistors become similar, so that itbecomes possible to provide a plurality of transistor circuits withlittle variance in voltage/current characteristics and thresholdcharacteristics on the same substrate.

According to a ninth aspect of the invention, the transistor circuitaccording to any of the above-noted first to seventh aspect, ischaracterized in that the transistors consist of bipolar transistorsrespectively, wherein the gate, source and drain correspond to a base, acollector and an emitter respectively.

According to the transistor circuit of the ninth aspect, the effect ofvoltage/current characteristics and threshold characteristics of thedriving bipolar transistor on a driving current can be compensated bythe compensating bipolar transistor. Particularly, as both bipolartransistors are manufactured in the same manufacturing process, thedegree of characteristic similarity between both transistors generallyincreases, so that it becomes possible to provide a plurality oftransistor circuits with little variance in voltage/currentcharacteristics and threshold characteristics.

According to a tenth aspect of the invention, the transistor circuitaccording to any of the above-noted first to ninth aspects, ischaracterized in that the input signals are voltage signals where thevoltage is controlled by an input signal source and that the drivingtransistor, wherein one of the first source and first drain is connectedto a current-controlled element, and electric current flowing to thecurrent-controlled element is controlled by controlling the conductance.

According to the transistor circuit of the tenth aspect of theinvention, as the voltage signals where a voltage is controlled by aninput signal source are supplied through the compensating transistor asinput signals, conductance between the first source and first drain iscontrolled in response to the change in voltage of these voltage signalsin the driving transistor. As a result, the current-controlled elementconnected to one of the first source and first drain iscurrent-controlled. Thus, it becomes possible to current-drive thecurrent-controlled element by the input signals of a relatively lowvoltage. Moreover, it becomes possible to current-control a plurality ofcurrent-driven elements with good precision in response to voltagesignals without being dependent on the variance in voltage/currentcharacteristics and thresholds between a plurality of drivingtransistors.

According to this invention, a display panel is provided which ischaracterized in that it includes the above-noted tenth transistorcircuit of this invention respectively and has a plurality of pictureelements arranged in a matrix, and that current-controlledlight-emitting elements are provided respectively to the plurality ofpicture elements as the current-controlled elements.

According to the display panel, as input signals are provided throughthe compensating transistor at each picture element, thecurrent-controlled light-emitting elements are current-controlled inresponse to the voltage of these input signals by the drivingtransistor, so that the brightness of the current-controlledlight-emitting elements can be controlled with good precision withoutbeing dependent on the variance in voltage/current characteristics andthreshold characteristics among the driving transistors, and that theunevenness of brightness can be reduced over the entire screen displayarea of the display panel. Moreover, by increasing the gate voltage ofthe driving transistor with the compensating transistor, thecurrent-controlled light-emitting elements can be controlled by theinput signals of a relatively low voltage.

According to this invention, an electronic apparatus having theabove-noted display panel is provided.

According to such an electronic apparatus, since it has theabove-described display panel, an electronic device can be realized thathas little unevenness in brightness over the entire surface of thedisplay panel and can be driven at a relatively low voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram in one embodiment of a transistor circuit ofthe invention.

FIG. 2(A) is a timing chart of various signals in a transistor circuitusing p-channel transistors, and FIG. 2(B) is a timing chart of varioussignals in a modified embodiment of the transistor circuit usingn-channel transistors.

FIG. 3(A) is a characteristic diagram showing the thresholdcharacteristics in a comparative example having a driving TFT, and FIG.3(B) is a characteristic diagram showing the threshold characteristicsin the embodiment having a compensating TFT and a driving TFT.

FIG. 4 is a characteristic diagram showing various cases of thefluctuation in driving current Id in response to the variance ΔVth ofthresholds.

FIG. 5(A) is a timing chart showing dropping voltage operations by acompensating TFT when the reset signal Vrsig is set at 5V in theembodiment, and FIG. 5(B) is a timing chart showing dropping voltageoperations by the compensating TFT when the reset signal Vrsig is set at0V.

FIG. 6 is a circuit diagram in another embodiment of a transistorcircuit of the invention.

FIG. 7 is a planar view showing an entire structure in one embodiment ofa display panel of the invention.

FIG. 8 is a planar view of one picture element of the display panel ofFIG. 7.

FIG. 9(A) is a cross-sectional view taken on line A-A′ of FIG. 8; FIG.9(B) is a cross-sectional view taken on line B-B′; and FIG. 9(C) is across-sectional view taken on line C-C′.

FIG. 10 is a circuit diagram of four adjoining picture elements in thedisplay panel of FIG. 7.

FIG. 11 is a block diagram showing a schematic structure in oneembodiment of an electronic apparatus of this invention.

FIG. 12 is a front view of a personal computer as an example of anelectronic apparatus.

FIG. 13 is a perspective diagram showing a liquid crystal device using aTCP as another example of an electronic apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The operation of this invention and other benefits will be made clear bythe embodiments explained below. The embodiments of this invention willbe explained below with reference to the drawings.

(Transistor Circuit)

First, the embodiment of a transistor circuit of this invention isexplained with reference to FIG. 1 and FIGS. 2(A)-2(B). FIG. 1 is acircuit diagram of a transistor circuit in the embodiment, and FIG. 2(A)and FIG. 2(B) are timing charts showing the timing and voltage ofvarious signals in the transistor circuit respectively.

In FIG. 1, a transistor circuit 100 may consist of a driving TFT 110 (Pchannel type), a compensating TFT 120 (P channel type), a resetting TFT130 (N channel type) and a switching TFT 140 (N channel type). Thestructure of each transistor will be sequentially explained below.

First, the driving TFT 110, as an example of driving transistors, isconstructed so as to control conductance between a source 112 and adrain 113 in response to a gate voltage Vg applied to a gate 111 basedon input signals supplied through the switching TFT 140 and thecompensating TFT 120.

The compensating TFT 120, as an example of compensating transistors, hasits gate 121 connected to one of a source 122 and a drain 123 (drain 123in the case of FIG. 1). In other words, the compensating TFT 120 isso-called diode-connected. Moreover, the compensating transistor 120 isconnected to the gate 111 in an orientation so as to supply inputsignals to the gate 111 through the source 122 and the drain 123 and toallow the gate 111 to move electric charge into a direction to lowerconductance (the side of drain 123 in FIG. 1).

The resetting TFT 130, an example of resetting devices, has one of asource 132 and a drain 133 (drain 133 in FIG. 1) connected to the gate111, and reset signals at voltage Vrsig (called reset signals Vrsighereafter) are supplied to the gate 111 through the source 132 and thedrain 133 when reset scanning signals at voltage Vrscan (called resetscanning signals Vrscan hereafter) are supplied to the gate 131 as anexample of reset timing signals before the supply of input signals Vsig.

Also, the switching TFT 140, an example of switching transistors, isconnected between an input signal source and the compensating TFT 120 soas to supply input signals at voltage Vsig (called input signals Vsighereafter) to the compensating TFT 120 through a source 142 and a drain143 when scanning signals at voltage Vscan (called scanning signalsVscan hereafter) are supplied to the gate 141 as an example of switchingtiming signals.

Moreover, one terminal of a current-controlled (current-driven) element500 such as an EL element is connected to the source 112 of the drivingtransistor 110, and negative power source −Vc with a predeterminedelectric potential is connected to another terminal of thiscurrent-controlled element 500. In addition, positive power source +Vcwith a predetermined electric potential is connected to the drain 113 ofthe driving transistor 110. Therefore, when conductance between thesource 112 and the drain 113 is controlled at the driving transistor110, driving current Id flowing through the current-controlled element500 is controlled (in other words, driving current Id varies in responseto conductance fluctuation).

Furthermore, a storage capacitor 160 is connected to the gate 111 of thedriving transistor 110. As a result, the once applied gate voltage Vg isheld by the storage capacitor 160.

Then, the operation of the transistor circuit 100 constructed as aboveis explained with reference to FIG. 1 along with FIGS. 2(A)-3.

As shown in FIG. 2(A) (this figure shows that a P channel type TFT isapplied to both the driving TFT 110 and the compensating TFT 120), theresetting TFT 130 will be in conductance when reset scanning signalsVrscan are input to the resetting TFT 130; and resetting signals Vrsigare then supplied to the gate 111 of the driving TFT 110, so that thegate voltage Vg of the gate 111 becomes almost the same as the voltageVrsig of these reset signals Vrsig. As a result, without being dependenton the level of voltage of input signals Vsig, the gate voltage Vg ofthe driving TFT 110 can be reset at a fixed voltage (in other words,voltage Vrsig) by the supply timing of reset scanning signals Vrsig.

Then, as scanning signals Vscan are supplied to the switching TFT 140after this resetting period, the switching TFT 140 will be inconductance and the driving signals Vsig are supplied to the gate 111 ofthe driving TFT 110 through the compensating TFT 120. In thisembodiment, the gate 121 is connected (in other words, diode-connected)to the drain 123 particularly in the compensating TFT 120 herein, sothat gate voltage Vg in the driving TFT 110, the P channel type TFT thatwill be in conductance by the application of negative voltage to thegate 111, is made lower than the voltage Vsig of data signals Vsig tothe negative voltage side only by a threshold voltage Vth2 level of thecompensating TFT 120. Then, the gate voltage Vg lowered as mentionedabove will be held in a driving period by the storage capacitor 160 evenafter the supply of scanning signals Vscan and input signals Vsig isstopped.

In addition, the period in which gate voltage Vg becomes the voltageVrsig of reset signals Vrsig is sufficient for the resetting period.Thus, the driving period can be set much longer than the resettingperiod, so that even if the driving TFT 110 is in conductance byresetting signals Vrsig in the resetting period, the effect on thedriving current Id flowing through the source 112 and the drain 113 ofthe driving TFT 110 in this period can be minimized to a negligibledegree.

As described above, according to this embodiment, gate voltage Vgrelative to input signals Vsig can rise only by a threshold voltage Vth2level of the compensating TFT 120, so that it becomes possible to carryout the same conductance control in the driving TFT 110 by using a lowerinput signal voltage Vsig compared with the case with no compensatingTFT 120.

Also, FIG. 2(B) is a timing chart where an N channel type TFT is appliedto both the driving TFT 110 and the compensating TFT 120. In this case,the gate voltage Vg at the driving TFT 110, the N channel type TFT thatwill be in conductance by the application of positive voltage to thegate 111, is made higher than the voltage Vsig of input signals Vsig tothe positive voltage side only by a threshold Vth2 level of thecompensating TFT 120 after being set at the voltage Vrsig of resetsignals Vrsig during resetting.

If input signals Vsig are directly input to the driving TFT 110 withoutgoing through the compensating TFT 120, in other words, when the voltageVsig of input signals Vsig is the same as the gate voltage Vg, thedriving current Id is boosted from a threshold voltage Vth1 of thedriving TFT 110 as shown in FIG. 3(A) (in this case, the driving TFT 110is an N channel TFT). For example, if the design standard value of thisthreshold voltage Vth1 is 2V, a variance in thresholds will be aboutseveral +V. Then, a variance in threshold voltage Vth1 in the drivingTFT 110 will appear directly as a variance in driving current Id.

On the contrary, in this embodiment, since input signals Vsig are inputto the driving TFT 110 through the compensating TFT 120, in other words,when the voltage Vsig of input signals Vsig is boosted only by thethreshold voltage Vth2 level of the compensating TFT 120 to become gatevoltage Vg, the threshold voltage Vth2 of the compensating TFT 120 andthe threshold voltage Vth1 of the driving TFT 110 are offset as shown inFIG. 3(B) (in this case, both the driving TFT 110 and the compensatingTFT 120 are N channels TFTS) and the threshold voltage Vth of the inputsignals Vsig to the entire transistor circuit 100 then becomesapproximately zero. Moreover, particularly when both threshold voltagesVth1 and Vth2 are nearly the same, this threshold voltage Vth becomesapproximately zero. Thus, equalizing threshold voltage Vth1 to Vth2 canbe relatively easily carried out e.g., by applying the same conductivetype TFT to the driving TFT 110 and the compensating TFT 120 in anadjoining position on the same semiconductor substrate.

As constructed above, in both TFTs, the thickness of thin gateinsulating films, semiconductor films, and the like, the planar shapesof each component such as a channel length, impurity concentration inregions for forming channels, source regions and drain regions,temperature during operation and the like can easily become the same, sothat the threshold voltage Vth1 and Vth2 of both TFTs can be completelyor almost completely equalized. In addition, in making thresholdcharacteristics similar, it is better to make channel lengths the same,but channel widths do not have to be the same.

Thus, according to this embodiment, by setting the thresholdcharacteristics and voltage/current characteristics of the driving TFT110 and the compensating TFT 120 close to each other (ideally the same),it is possible to set the threshold voltage Vth of input signals Vsigsupplied to the driving current Id to approximately zero (ideally equalto zero).

Moreover, as seen from FIG. 3(A) and FIG. 3(B), in manufacturing aplurality of transistor circuits 100, even if threshold voltage Vth1 ateach driving TFT 110 varies from each other, the threshold voltage Vthof each transistor circuit 100 is approximately zero by the operation ofeach compensating TFT 120 without being dependent on the level of thisthreshold voltage Vth1. In other words, a plurality of transistorcircuits 100 with a constant threshold voltage Vth can be manufactured.This is particularly useful for a display panel and the like where avariance in threshold voltage Vth among a plurality of transistorcircuits 100 is a problem as described below. Also, it is much easier toequalize the threshold voltage Vth1 of the driving TFT 110 and thethreshold voltage Vth2 of the compensating TFT 120 that are a mutuallyadjoining pair at each transistor circuit 100 than to equalize thethreshold voltage Vth1 of two driving TFTs 110 that are separatelyarranged with a gap therebetween, so that it is possible to say that thestructure of compensating threshold voltage Vth1 in each transistorcircuit 100 by the compensating TFT 120 is extremely effective, so as toreduce a variance in threshold voltage Vth among a plurality oftransistor circuits 100 from each other.

As described above, according to this embodiment, even if a plurality ofdriving TFTs 110 with different threshold voltage Vth1 from a thresholdvoltage (for example, 2.5V) as a design standard level is used inpreparing a plurality of transistor circuits 100, it becomes possible toprovide a plurality of circuits 100 with little or no variance inthreshold voltage Vth. Therefore, the requirements for TFTs regardingvoltage/current characteristics are made easy, and it becomes possibleto improve yields and lower manufacturing costs.

In addition, as seen from FIG. 3(A) and FIG. 3(B), by equalizingthreshold voltages Vth1 and Vth2, the first effect where conductancecontrol at each driving TFT 110 can be carried out by using a highergate voltage Vg than the voltage Vsig of input signals Vsig and thesecond effect where a variance in threshold voltage Vth among aplurality of transistor circuits 100 are clearly achieved. However, evenwithout completely equalizing the threshold voltage Vth1 of the drivingTFT 110 and the threshold voltage Vth2 of the compensating TFT 120 ineach transistor circuit 100, both threshold voltages characteristicallywill offset each other, so that these first and second effects areachieved to some degree, based on the similarity of both thresholdvoltages.

In this embodiment, particularly, it is constructed so as to supplyreset signals Vrsig having a voltage in response to a higher conductancethan the maximum conductance controlled in response to input signalsVsig to the gate 111. Therefore, it becomes possible to supply inputsignals Vsig to the gate 111 through the compensating TFT 120 that isconnected to the gate 111 in an orientation, to permit electric chargeto move into a direction so as to lower this conductance afterresetting, without being dependent on the level of voltage Vsig of inputsignals Vsig. Also, in this embodiment, reset signals Vrsig are set at ahigher voltage than the maximum voltage of input signals Vsig by thethreshold voltage Vth2 level of the compensating TFT 120. Therefore,when input signals Vsig are input after resetting, a voltage higher thanthe voltage Vsig of input signals Vsig only by the threshold voltageVth2 level of the compensating TFT 120 can always be supplied to thegate 111 without being dependent on the level of the voltage Vsig ofinput signals Vsig and the threshold voltage Vth2 of the compensatingTFT 120.

Moreover, when the inversion of input signals Vsig is carried out asfrequently applied in conventional liquid crystal display elements, itis desirable that the above-noted reset signal Vsig relations areachieved in all input signals Vsig, including inverse input signals.

The effects of these reset signals Vrsig by voltage setting are examinedwith reference to FIGS. 4-5(B). Herein, FIG. 4 respectively shows thefluctuation in driving current relative to a variance ΔVth in thresholdvoltage from a design standard level that is, for instance, −2.5V (1)when input signals Vsig are supplied directly to the driving TFT 110without the compensating TFT 120 (characteristic curve C1), (2) wheninput signals Vsig are supplied to the driving TFT 110 through thecompensating TFT 120 at 5V of reset signal Vrsig (characteristic curveC2), and (3) when input signals Vsig are supplied to the driving TFT 110through the compensating TFT 120 with reset signal Vrsig at 0V(characteristic curve C3). Also, FIG. 5(A) shows the fluctuation rangeof the gate voltage Vg corresponding to the characteristic curve C2, andFIG. 5(B) shows the fluctuation range of the gate voltage Vgcorresponding to the characteristic curve C3. In addition, herein, Vsigis 7.5V; +Vc is 10V; and −Vc is 5V.

In FIG. 4, as indicated with the characteristic curve C1, the varianceΔVth in threshold voltage clearly appears directly as the variance indriving current Id in the case of having no compensating TFT 120.

As illustrated with the characteristic curve C2, when the compensatingTFT is used at 5V of reset signal Vrsig, the variance ΔVth in thresholdvoltage is significantly compensated on the plus side, but appears asthe variance in driving current Id at the minus side. This is because,as shown in FIG. 5(A), on the minus side, the gate voltage Vg cannot bemade lower (or compensated) than the input signals Vsig by the thresholdvoltage Vth2 level to the negative voltage side, when the input signalsVsig are input after resetting. This is because the compensating TFT 120acting as a diode can make the gate voltage Vg closer to the inputsignals Vsig from the reset signals Vrsig, but cannot do the opposite.

Also, as shown with the characteristic curve C3, when the compensatingTFT is used with 0V of reset signal Vrsig, the variance ΔVth ofthreshold voltage hardly appears as the variance in driving current Id.This is because, as shown in FIG. 5(B), the gate voltage Vg can be madelower (or compensated) than the input signals Vsig only by thresholdvoltage Vth level to the negative voltage side, when the input signalsVsig are input after resetting. Moreover, if Vsig=7.5V applied herein isconsidered as the minimum electric potential of input signals Vsig, theabove-noted examination is realized to make sure that all Vsig can becompensated.

As described above, in this embodiment, without being dependent on thelevel of input voltage Vsig and threshold Vth2 of the compensating TFT110, a voltage Vg that is lower than the voltage of the input signalsVsig only by the threshold voltage Vth2 level of the compensating TFT120 can be applied to the gate 111 of the driving TFT 110.

In addition, in FIG. 2(A) and FIG. 2(B), the gate voltage Vg is held bythe storage capacitor capacity 160 during the driving period. Therefore,by the storage capacitor 160, a variance in holding characteristics ofthe gate voltage Vg among a plurality of transistor circuits 100 can bealso reduced (compensated).

As explained with reference to FIG. 1 to FIG. 5B, according to thetransistor circuit 100 of this embodiment, the current-controlledelement 500 such as an EL element can be current-driven by input signalsVsig at a relatively low voltage; and moreover, without being dependenton a variance in voltage/current characteristics and thresholdcharacteristics among a plurality of driving TFTs 110, a plurality ofcurrent-controlled elements 500 can be current-controlled with goodprecision in accordance with the voltage of input signals Vsig.

Moreover, the example shown in FIG. 1 is constructed with the mixture ofa P channel type TFT and an N channel type TFT, however, every TFT canbe N channel type TFTs or all TFTs can be P channel type TFTs. However,in consideration that the voltage/current characteristics and thresholdcharacteristics of the driving TFTs 110 are compensated by thecompensating TFT 120, it is advantageous to construct these driving TFTs110 and compensating TFTs 120 by the same process as the same type TFTs.Particularly, if both TFTs are formed in the same film forming process,the degree of characteristic similarities between both TFTs generallyincreases, so that it becomes possible to provide the transistor circuit100 on the same substrate with little or no variance in voltage/currentcharacteristics and threshold characteristics. On the other hand, theresetting TFT 130 and the switching TFT 140 can be either a P channeltype TFT or an N channel type TFT without being dependent on whether thedriving TFT 110 is a P channel type TFT or N channel type TFT. However,it is often advantageous in manufacturing when all TFTs are of the sametype.

Also, each type of TFTs 110-140 in this embodiment may be any type offield effect transistor (FET) such as joining type, parallel/serialconnection type, and the like.

Furthermore, as shown in FIG. 6, the above-noted transistor circuit mayconsist of bipolar transistors. In this case, by corresponding theabove-mentioned gate, source and drain to a base, an emitter and acollector respectively, a driving transistor 110′ is constructed from abipolar transistor, and at the same time, a compensating transistor 120′is constructed from a bipolar transistor, thus providing a transistorcircuit 100′. Generally, in the case of bipolar transistors, thevariance in threshold voltage with e.g., 0.7V as a center is smallerthan that of TFTs, however, even if constructed as above, the effect ofvariance in voltage/current characteristics and thresholdcharacteristics in the driving transistor 110′ on the driving current Idcan be compensated by the compensating transistor 120′. Furthermore,driving can be carried out by the driving transistor 110′ at arelatively low voltage. Particularly, when the driving transistor 110′and the compensating transistor 120′ are manufactured in the samemanufacturing process, the degree of characteristic similarities betweenboth transistors generally increases, so that it becomes possible toprovide a plurality of transistor circuits 100′ with little or reducedvariance in voltage/current characteristics and thresholdcharacteristics.

As the current-controlled element 500 in the embodiment mentioned above,various elements including current-controlled light-emitting elementssuch as an organic EL element and an inorganic EL element, acurrent-controlled heat transfer element, and the like, are included.

(Display Panel)

The embodiments of a display panel of this invention is explained withreference to FIG. 7 to FIG. 10. FIG. 7 is a block diagram showing theentire structure of a display panel; FIG. 8 is a planar view of onepicture element in the display panel; FIG. 9(A), FIG. 9(B) and FIG. 9(C)are respectively a cross-sectional view on line A-A′, a cross-sectionalview on line B-B′ and a cross sectional view on line C-C′ thereof; andFIG. 10 is a circuit diagram of four picture elements adjoining eachother.

The display panel in this embodiment includes the above-noted transistorcircuits of this invention, respectively, and a plurality of pictureelements arranged in a matrix; and at the plurality of picture elements,EL elements 50 are arranged respectively as an example ofcurrent-controlled light-emitting elements.

As shown in FIG. 7, a display panel 200 has a TFT array substrate 1, aplurality of data lines 11 extending in the Y direction and arranged inthe X direction in a picture display area wherein a plurality of pictureelements 2 are arranged in a matrix on the TFT array substrate, aplurality of scanning lines 12 extending respectively in the X directionand arranged in the Y direction, and a plurality of common electricwires 13 arranged in parallel to the plurality of data lines 11. Thedisplay panel 1 further has a data line driving circuit 21 around thepicture display area for supplying data signals to each data line 11, apair of scanning line driving circuits 22 for supplying scanning signalsto each scanning line 12, and an inspecting circuit 23 for inspectingconductance failure, insulation failure, defects of elements, and thelike in each picture element 2. In addition, in this embodiment, eachdriving circuit is formed on the TFT array substrate 1 along with apicture element 2 in the same process, but it can be a circuit that isnot formed on the TFT array substrate 1 or may be formed in a differentprocess from the picture element 2.

As shown in FIG. 8, at each picture element 2, the driving TFT 110, thecompensating TFT 120, the resetting TFT 130, the switching TFT 140 andthe storage capacitor 160 that are explained above with reference toFIG. 1 to FIG. 6 are arranged. Moreover, a scanning line 12 b in aprevious stage becomes the wiring for reset scanning signals Vrscan inFIG. 1; a scanning line 12 a in this stage becomes the wiring forscanning signals Vscan and for reset signals Vrsig in FIG. 1; and a dataline 11 a in this stage becomes the wiring for input signals Vsig (datasignals) in FIG. 1. Furthermore, the common electric wire 13 isconnected to a positive power source +V; an EL element 50 is connectedbetween the driving TFT 110 and a counter electrode to be mentionedlater; and the counter electrode is connected to a negative power supply−V.

As shown in FIG. 9(A), the switching TFT 140, the compensating TFT 120and the storage capacitor 160, along an A-A′ cross section in FIG. 8,consist of a semiconductor film (polysilicon film) 4 on the TFT arraysubstrate 1, a gate insulating film 5 consisting of a silicon oxide filmor a silicon nitride film, a Ta (tantalum) film 6, a first interlayerinsulating film 7 consisting of a silicon oxide film or a siliconnitride film, and an Al film 8. In addition, instead of the Ta film forforming gate electrodes, a low-resistance polysilicon film may beformed.

More specifically, the switching TFT 140 is a top gate type TFT having agate 141 made of the polysilicon film 6, and is formed as an N channeltype TFT having a semiconductor layer 4 countering the gate 141 throughthe gate insulating film 5 as a channel forming area and having a source142 and a drain 143 that are doped at high concentration in the n typeon both sides of the area. Also, the source 142 is connected to a dataline 11 a made of an Al film 8 through contact holes formed in the gateinsulating film 5 and the first interlayer insulating film 7. Moreover,the drain 143 is connected to the compensating TFT 120 through contactholes formed in the gate insulating film 5 and the first interlayerinsulating film 7 as well as the Al film 8.

The compensating TFT 120 is a top gate type TFT having a gate 121 madeof a Ta film 6, and is formed as a P channel type TFT having asemiconductor film 4 countering the gate 121 through the gate insulatingfilm 5 as a channel forming area and having a source 122 and a drain 123that are doped at high concentration in the p type on both sides of thearea. Also, the TFT is connected to the switching TFT 140, the storagecapacitor 160 and the gate 111 of the driving TFT 110 through thecontact holes formed in the gate insulating film 5 and the firstinterlayer insulating film 7 and the Al film 8.

In addition, the storage capacitor 160, so as to have a double capacitorstructure, is formed in that the semiconductor film 4, the Ta film 6 andthe Al film 8 are counter-arranged with the gate insulating film 5 andthe first interlayer insulating film 7 respectively therebetween. Also,the semiconductor film 4 constituting a storage capacitor is connectedto the Al film 8 through the contact holes formed in the gate insulatingfilm 5 and the first interlayer insulating film 7; and the Ta film 6constituting a storage capacitor is connected to the Al film 8 throughthe contact holes formed in the first interlayer insulating film 7.

As shown in FIG. 9(B), the resetting TFT 130, along a B-B′ cross sectionin FIG. 8, consists of a semiconductor film 4, a gate insulating film 5,a Ta film 6, a first interlayer insulating film 7 and an Al film 8 on aTFT array substrate 1.

More specifically, the resetting TFT 130 is a top gate type TFT having agate 131 made of a Ta film 6, and is formed as an N channel type TFThaving a semiconductor layer 4 facing the gate 131 through the gateinsulating film 5 as a channel forming area and having a source 132 anda drain 133 that are doped at high concentration in the n type on bothsides of the area. Also, the source 132 and the drain 133 are connectedrespectively to a scanning line 12 a in this stage made of a Ta film 6and the gate 111 of the driving TFT 110 through the contact holes formedin the gate insulating film 5, the first interlayer insulating film 7and the Al film 8.

Moreover, as shown in FIG. 9(C), the driving TFT 110, along a C-C′ crosssection in FIG. 8, consists of a semiconductor film 4, a gate insulatingfilm 5, a Ta film 6, a first interlayer insulating film 7 and an Al film8 on a TFT array substrate 1. Also, on a second interlayer insulatingfilm 9, an ITO film 51 is formed that is connected to the drain 113 ofthe driving TFT 110 through contact holes and the Al film 8, and an ELelement 50 is formed thereon. On the other hand, the source 112 of thedriving TFT 110 is connected to a common electric wire 13 made of the Alfilm 8 through contact holes. Also, EL elements 50 at adjoining pictureelements 2 are separated from each other by electrically insulatingbanks 52. Preferably, the banks have a shielding property. The banks 52are made of, for instance, a shielding resist, and the bank 52 may beprovided even at a peripheral parting area surrounding the picturedisplay area of the display panel 200. In addition, on the EL element50, a counter electrode (top electrode) 56 is arranged that is made of alow-resistance metal such as Al or ITO, and the like.

As shown in FIG. 10, the display panel 200 particularly has a structurewherein positive power source +V is supplied to both picture elements 2which are mutually adjoining in the X direction by the common electricwire 13; and compared with the case wherein power source wiring forsupplying positive power source +V is simply provided for each ofpicture elements 2, the number of power source wiring is about ½.Moreover, having a structure wherein reset scanning signals Vrscan inputto the gate 131 of the resetting TFT 130 are supplied by a scanning line12 b in the previous stage and reset signals Vrsig input to theresetting TFT 130 are supplied by a scanning line 12 b in the currentstage, the number of signal wiring is reduced compared with the casewherein wiring only for reset scanning signals Vrscan and wiring onlyfor reset signals Vrsig are provided. Therefore, without increasing thenumber of power source wiring and signal wiring, a space for thecompensating TFT 120 and the resetting TFT 130 that is not provided inconventional display panels can be kept. There is no doubt that theideas of this invention are applicable to the ones, different from thisembodiment, wherein patterns are made the same for each picture elementby providing a common electric wire per picture element or whereinwiring only for reset scanning signals Vrscan and wiring only for resetsignals Vrsig are provided.

In addition, in the case of the display panel 200 wherein the ELelements 50 are used as current-driven light-emitting elements as inthis embodiment, unlike liquid crystal panels, and the like, the panelemits its own light in response to the increase in electric currentsupplied to the light-emitting elements without increasing the entirearea of picture elements, so that brightness necessary for picture imagedisplay can be obtained. Thus, as in this embodiment, it is possible tomaintain a space for forming various TFTs in a picture element 2 bysaving a wiring area, or a space for forming various TFTs in a pictureelement 2 may be kept by reducing the size of each EL element 50.

Next, the operation of the display panel 200 of this embodiment isexplained with reference to FIG. 7 and FIG. 10.

When scanning signals Vscan are supplied to a scanning line 12 b in aprevious stage from a scanning line driving circuit 22, they are inputto the gate 131 of the resetting TFT 130 in the current stage as resetscanning signals Vrscan in the current stage. At the same time, resetsignals Vrsig are supplied from the scanning line driving circuit 22 toa scanning line 12 a in the current stage, and the gate voltage Vg ofthe driving TFT 110 in the current stage becomes the electric potentialof reset signals Vrsig (see FIG. 2(A)). At this time, the reset signalsVrsig may be the same as the OFF-state electric potential of scanningsignals Vscan. When the scanning signals Vscan are continuously suppliedfrom the scanning line driving circuit 22 to the scanning line 12 a inthe current stage, they are then input to the gate 141 of the switchingTFT 140 in the current stage. At the same time, input signals Vsig (datasignals) are supplied from a data line driving circuit 21 to a data line11 a in the current stage, and this voltage Vsig is dropped only by athreshold voltage Vth2 of the compensating TFT 120 through the switchingTFT 140 and the compensating TFT 120, and is then supplied as a gatevoltage Vg to the gate 111 of the driving TFT 110 in the current stage(see FIG. 2(A)). As a result, in response to this dropped gate voltageVg, conductance between the source 112 and the drain 113 of the drivingTFT 110 is controlled between positive power source +V and negativepower source −V. The driving current Id flowing to the EL element 50 isthen controlled.

Therefore, a variance in threshold voltage Vth1 of the driving TFT 110at each picture element 2 is compensated by a threshold Vth2 of thecompensating TFT 120, and the variance in thresholds of data signalsVsig in response to the driving current Id among a plurality of pictureelements 2 is almost gone, so that even picture images are displayedwith even brightness over the entire picture display area of the displaypanel 200. It is also possible to control the driving current Id withdata signals Vsig having a relatively small voltage due to the droppingvoltage operation of the compensating TFT 120.

In the above-noted embodiment, the gate voltage Vg is reset by theresetting TFT 130 before input signals Vsig are supplied, however, forinstance, in the display period of a static picture, the control ofdriving current Id can be carried out over a plurality of frames by thesame input signals Vsig, so that it is unnecessary to carry outresetting operations for each scanning. Also, instead of theseelectrically reset signals Vrsig, the gate voltage Vg may be reset (tobe a predetermined reset voltage) by light irradiation. Furthermore,instead of the resetting TFT 130, reset signals Vrsig may be suppliedthrough the switching TFT 140 and the compensating TFT 120. On the otherhand, of course, the switching TFT 140 and switching operations will beunnecessary if switching such as active matrix driving is not carriedout.

(Electronic Apparatus)

Next, the electronic apparatus of the embodiment having the displaypanel 200 which was explained above in detail will be explained withreference to FIG. 11 to FIG. 13.

First, FIG. 11 shows the schematic structure of an electronic apparatushaving the display panel 200 as mentioned above.

In FIG. 11, the electronic device includes a display information outputsource 1000, a display information processing circuit 1002, a drivingcircuit 1004, a display panel 1006, a clock generating circuit 1008 anda power source circuit 1010.

The display panel 200 in the above-noted embodiment is equivalent to thedisplay panel 1006 and the driving circuit 1004 in this embodiment.Therefore, the driving circuit 1004 may be installed on a TFT arraysubstrate of the display panel 1006, and moreover, the displayinformation processing circuit 1002, and the like may be installed.Alternatively, the driving circuit 1004 may be fixed externally onto aTFT array substrate on which the display panel 1006 is installed.

The display information output source 1000 includes a memory such as ROM(Read Only Memory), RAM (Random Access Memory) and an optical diskdevice, a tuning circuit for tuning television signals and thenoutputting the signals, and the like; and based on clock signals fromthe clock generating circuit 1008, display information such as thepicture image signals of a predetermined format is output to the displayinformation processing circuit 1002. The display information processingcircuit 1002 includes various conventional processing circuits such asan amplifying/inversion circuit, a phase developing circuit, a rotationcircuit, a gamma control circuit and a clamp circuit; and digitalsignals are sequentially formed from display information that is inputbased on clock signals and are then output to the driving circuit 1004along with clock signals CLK. The driving circuit 1004 drives thedisplay panel 1006. The power source circuit 1010 supplies apredetermined power source to each circuit mentioned above.

Next, the specific examples of the electronic apparatus prepared asabove are shown respectively in FIG. 12 and FIG. 13.

In FIG. 12, as another example of the electronic apparatus, a multimedialaptop personal computer (PC) 1200 has the above-noted display panel 200in a top cover case 1206, and further includes a main body 1204 having aCPU, a memory, a modem, and the like and a built-in keyboard 1202.

Also, as shown in FIG. 13, in the case of a display panel 1304 with nobuilt-in driving circuit 1004 and display information processing circuit1002, an IC1324 containing the driving circuit 1004 and the displayinformation processing circuit 1002 is physically and electricallyconnected to a TCP (Tape Carrier Package) 1320 through an anisotropicconductive film 1322 arranged at the periphery of the TFT arraysubstrate 1, and can be manufactured, sold, used, etc. as a displaypanel.

As explained above, according to this embodiment, various electronicapparatuses are provided that can be driven at a relatively low voltageand with little unevenness in brightness over the entire surface of adisplay panel.

According to the transistor circuits of this invention, the gate voltagecan be reduced or increased relative to the voltage of input signalsonly by a threshold voltage of a compensating transistor, so thatconductance control in the driving transistor can be carried out by adropped voltage of input signals. Moreover, by making the thresholdcharacteristics and voltage/current characteristics of a compensatingtransistor and a driving transistor similar, the threshold voltage ofinput signals to driving current can become approximately zero.Furthermore, in the case a plurality of the transistor circuits isprepared by applying a plurality of driving transistors with differentthreshold characteristics, even if a plurality of driving transistorswith many different threshold voltages are applied, in other words, aplurality of driving transistors having various threshold voltagesrelative to a design standard level, it is also possible to provide aplurality of transistor circuits with almost no variance or no varianceat all in threshold voltage in the plurality of transistor circuits.

According to the display panel of this invention, a picture imagedisplay with reduced unevenness in brightness is achieved by applyinglow voltage input signals.

INDUSTRIAL APPLICABILITY

A display panel is provided that can display picture images with reducedunevenness in brightness, from the transistor circuits of thisinvention; and the display panel is useful for electronic devices suchas laptop personal computers (PC), televisions, view finder or monitordisplay-type video tape recorders, car navigation devices, electronicnotebooks, calculators, word processors, engineering workstations (EWS),cellular phones, TV telephones, POS terminals, pagers, devices withtouch panels, and the like.

The invention claimed is:
 1. A driving method for a display having a transistor circuit that includes a light-emitting element, and a driving transistor controlling a current flowing through the light-emitting element, the method comprising: compensating a data signal for a threshold voltage of the driving transistor by passing the data signal through a diode-connected transistor configuration when the data signal is supplied to the transistor circuit; and controlling the current flowing through the light-emitting element by the driving transistor, a gate voltage of the driving transistor is set at a level being obtained by the compensating, wherein the diode-connected transistor configuration is defined as any transistor, having a gate and at least one of a source and a drain, while its gate is connected to either its source or its drain.
 2. The driving method of claim 1, further comprising a step of resetting the gate voltage of the driving transistor before compensating for the threshold voltage of the driving transistor.
 3. A driving method for a display including a scanning line, a data line, and a pixel including a light-emitting element and a transistor circuit including a driving transistor controlling a current flowing through the light-emitting element, and a switching transistor connected between the data line and the driving transistor, the method comprising: compensating a data signal for a threshold voltage of the driving transistor by passing the data signal through a diode-connected transistor configuration when the switching transistor is turned on based on a scanning signal supplied from the scanning line, for supplying the data signal to a gate of the driving transistor from the data line; and controlling the current flowing through the light-emitting element by the driving transistor, a voltage of the gate of the driving transistor being set at a level obtained by the compensating, wherein the diode-connected transistor configuration is defined as any transistor, having a gate and at least one of a source and a drain, while its gate is connected to either its source or its drain.
 4. The driving method according to claim 3, further comprising supplying a reset signal to the transistor circuit before supplying the data signal to the transistor circuit.
 5. A driving method for a display including a light-emitting element and a transistor circuit that includes a driving transistor controlling a current flowing through the light-emitting element, the method comprising: compensating a data signal for a threshold voltage of the driving transistor by passing the data signal through a diode-connected transistor configuration when the data signal is supplied to the transistor circuit; and controlling the current flowing through the light-emitting element by the driving transistor, a gate voltage of the driving transistor is obtained based on the data signal and the threshold voltage, wherein the diode-connected transistor configuration is defined as any transistor, having a gate and at least one of a source and a drain, while its gate is connected to either its source or its drain.
 6. The driving method according to claim 3, the data signal being supplied to a gate of the driving transistor through a compensating transistor. 